bjoernager/rust
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preserve bindings order for Some

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This commit is contained in:
Vishnunarayan K I 2020-11-03 12:15:41 +05:30
parent 6bdce7bedd
commit f422e811e4
19 changed files with 253 additions and 272 deletions
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33
compiler/rustc_mir_build/src/build/matches/simplify.rs
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@ -45,6 +45,26 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
) -> bool {
// repeatedly simplify match pairs until fixed point is reached
debug!("simplify_candidate(candidate={:?})", candidate);
// exisiting_bindings and new_bindings exists to keep the semantics in order
// reversing the binding order for bindings after `@` change binding order in places
// it shouldn't be changed, for example `let (Some(a), Some(b)) = (x, y)`
//
// To avoid this, the binding occurs in the following manner:
// * the bindings for one iteration of the following loop occurs in order (i.e. left to
// right)
// * the bindings from the previous iteration of the loop is prepended to the bindings from
// the current iteration (in the implementation this is done by mem::swap and extend)
// * after all iterations, these new bindings are then appended to the bindings that were
// prexisting (i.e. `candidate.binding` when the function was called).
//
// example:
// candidate.bindings = [1, 2, 3]
// binding in iter 1: [4, 5]
// binding in iter 2: [6, 7]
//
// final binding: [1, 2, 3, 6, 7, 4, 5]
let mut exisiting_bindings = mem::take(&mut candidate.bindings);
let mut new_bindings = Vec::new();
loop {
let match_pairs = mem::take(&mut candidate.match_pairs);
@ -52,13 +72,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
if let [MatchPair { pattern: Pat { kind: box PatKind::Or { pats }, .. }, place }] =
*match_pairs
{
exisiting_bindings.extend_from_slice(&new_bindings);
mem::swap(&mut candidate.bindings, &mut exisiting_bindings);
candidate.subcandidates = self.create_or_subcandidates(candidate, place, pats);
return true;
}
let mut changed = false;
for match_pair in match_pairs {
match self.simplify_match_pair(match_pair, candidate, &mut new_bindings) {
match self.simplify_match_pair(match_pair, candidate) {
Ok(()) => {
changed = true;
}
@ -80,11 +102,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// let z = x.copy_field;
// let y = x;
// }
new_bindings.extend_from_slice(&candidate.bindings);
candidate.bindings.extend_from_slice(&new_bindings);
mem::swap(&mut candidate.bindings, &mut new_bindings);
new_bindings.clear();
candidate.bindings.clear();
if !changed {
exisiting_bindings.extend_from_slice(&new_bindings);
mem::swap(&mut candidate.bindings, &mut exisiting_bindings);
// Move or-patterns to the end, because they can result in us
// creating additional candidates, so we want to test them as
// late as possible.
@ -124,7 +148,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
&mut self,
match_pair: MatchPair<'pat, 'tcx>,
candidate: &mut Candidate<'pat, 'tcx>,
bindings: &mut Vec<Binding<'tcx>>,
) -> Result<(), MatchPair<'pat, 'tcx>> {
let tcx = self.hir.tcx();
match *match_pair.pattern.kind {
@ -152,7 +175,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
}
PatKind::Binding { name, mutability, mode, var, ty, ref subpattern, is_primary: _ } => {
bindings.push(Binding {
candidate.bindings.push(Binding {
name,
mutability,
span: match_pair.pattern.span,